Underwire Case is a thin tube into which the underwire enters. It is used so that there is no direct contact of the 'hard' plastic tube with the body. It is made of satin jersey or velor fabric and it is possible to install single or double nylon reinforcement for better grip. Available with one gusset, to better follow the curve under the bust, or with two gussets for side reinforcement and in a variety of widths (8mm - 14mm), depends on your needs.